Hi. I've enjoyed the multiple, informative, and entertaining tutorials that Arduino enthusiasts have put on the web. Yall cover many details that a rank newbie might not know. One possible oversight is the breadboard. FWIW, I have a working project now:

http://www.youtube.com/watch?v=YCBD9QhsvlE

I had set up the Parallax Ping system and was not getting any sensible data out of the system. I was using some breadboard that I'd picked up somewhere. The boards have columns of around 5 holes, then a gap of a cm, then another 5 holes (don't have it in front of me right now). Somehow I had the presumption that it the entire column was connected. So I would generally set up pairs of wires across the gap.

What was funny in my case was that the system with this incorrectly wired sensor did respond to having one's hand in front of it, just inversely and not the right number. Like 41 inches pointed at a wall and 50 with your hand in front of it. The numbers weren't always repeatable but with dozens of hand wavings, I got a different number instantaneously upon changing my hand position. Anyway, my evil genius 11 year old son spotted that I had set up the wires differently (okay, incorrectly) compared to one YouTube tutorial. I guess what was fascinating is that the system gave any input at all. I wonder if this means that these cheap breadboards are leaky. Is perhaps the lesson not that you may place wires across the gap but that you must not?

The breadboard does NOT connect columns across the gap - but free floating (non pulled up/pulled down) pins can easily read random numbers, which you were probably seeing. These numbers are somewhat repeatable due to capacitance in the surroundings, which changes when you shift your hand. You can most easily observe this by printing out 'analogRead' values of an analog pin connected to the breadboard - there will be a noticeable shift as you move your hand further/closer to the board.

Your best learning experience would be to take your digital multimeter (if you don't have one, you must get one, now!) and put it into continuity mode (where it beeps if there is a connection path) and learn how all the solder-less holes are interconnected or not. Check the vertical power strips also as some connect the whole vertical length and others only go partially half way.

Learning electronics is also about about learning to ask yourself questions and coming up with non-distructive testing methods to answer your own questions. The lessons learned that way are bound to be better remembered then just reading about them.

A digital volt meter is an essential and wonderful tool for for learning as well as troubleshooting, no one should be without one in this hobby.

Oh my, that's it! Capacitance! Does make for an idea for a new sensor! It was so simplistic that I presumed I knew how it was built. Then much later I saw Bre Pettis' "Intro to Breadboards".

Thanks most kindly for all the very informative replies. In college, I was in a department in college of engineering, a (non-EE) department where the EE Department Chairman limited the number of EE classes we could take. He didn't want the university to turn out any half-arsed EE's. I'm afraid that's exactly what I have become. So while my day job actually involves debug of (nano &) microelectronics, I never played with breadboards until I started with Arduino.

One thing to remember about breadboards is that they can only be used for (essentially) low speed circuits; discrete component RF designs tend to be hit or miss (and for certain RF designs, forget it). Also, some components that you would think would be OK on a breadboard tend to be finicky - the LM386 is one of those...

I will not respond to Arduino help PM's from random forum users; if you have such a question, start a new topic thread.

Here is my equally tiny breadboard. I used its adhesive backing on a project (can you find it?) and when I broke it off the back plane (just paper) fell off. You can see very clearly how the tie points are connected! The domes are rubber feet so the board wouldn't easily short itself when it's on metal surface.